Existing AS-levels will be retained as standalone courses but results will no longer count towards the full A-level.

Ministers insist the changes – affecting up to 300,000 students a year – will create more time for teaching and ensure teenagers are better prepared for the demands of higher education.

But the move has angered Cambridge which currently relies on results at the end of the AS year to award provisional places.

In today’s letter, 40 admissions tutors from across Cambridge claim that AS results are more accurate than using GCSE scores, teachers’ predictions of pupils' ability or separate entry tests set by the university itself.

“Good results give students from all backgrounds the confidence to compete for a place at highly selective universities, including our own,” the letter says. “They reduce reliance upon grade predictions and enable schools to hold the line in the face of pressure to raise predicted grades unrealistically.”

Earlier this week, it emerged that the university was considering reintroducing its own Cambridge-wide admissions test – dropped in the 1980s – to replace AS results.

But the letter – signed by Steve Watts, chairman of the Cambridge admissions forum, Mike Sewell, director of admissions, and representatives of 29 Cambridge colleges – appeared to downplay the suggestion.

“AS marks are the best indicator of a student’s success at Cambridge,” it says. “Neither GCSEs nor admissions tests come close to matching the effectiveness of AS marks in this regard. If AS-levels disappear, university entry will become less fair.”

Dr Sewell told the Telegraph that the number of students applying to Cambridge had soared from 10,000 to 16,000 since the introduction of AS-levels and feared that numbers may fall back if the exams are scrapped.

He said many other universities used AS results in some form during the admissions process and rejected claims that abolition of the exams would free up more teaching time.

“It’s a false assumption,” he said. “What will happen is that schools will simply replace AS with mock exams that are internally moderated.”

But a senior Department for Education source insisted the comments from admissions officers clashed with those often made by senior academics.

"We are restoring the A-level to a two-year course partly because of repeated complaints – including from Oxbridge and Imperial – that A-levels no longer prepare pupils properly for advanced study," the source said.

"Academics routinely complain that they are prevented from speaking out by university authorities terrified of criticism over 'access'. We are trying to limit the damaging influence of Whitehall and politicians on exams over 30 years but if Cambridge University want to set up their own exams, then it would be very welcome."